A. c. control circuit

Claim 1

An a.c. control circuit including means for producing sine wave programming drive signals insensitive to electrical variables other than predetermined program reference variables comprising means for connecting said sine wave drive signal producing means to a d.c. program reference source having a program reference control voltage for programming the voltage of said a.c. control circuit, a d.c. operational amplifier having an input energized by connection through said connecting means to said d.c. program reference source and an output to provide an amplified program reference control voltaGe and also connected to provide a large negative feedback to said operational amplifier, an a.c. frequency-reference transformer having a primary with an input connection for energization by a main a.c. power source and a secondary output, a chopper having a d.c. input connected to said operational amplifier output and a chopping drive signal circuit connected to said a.c. frequency-reference transformer output, said chopper having an output providing a square wave signal with a peak-to-peak amplitude in accordance with said d.c. operational amplifier output program-reference control voltage and a frequency equal to and 180* out of phase with the main a.c. power source frequency, a sharp twin-T notch filter tuned sharply to the frequency of the main a.c. power source, means including an operational amplifier active filter having a negative feedback connection and an input drive circuit coupled to said chopper output through said sharp notch filter connected in said negative feedback connection and having an output providing a stable and drift-free sine wave output control voltage having a frequency synchronous with and in phase with the main a.c. power source frequency and a peak-topeak amplitude directly responsive to the peak-to-peak amplitude of said chopper square wave output; and a program controlled power supply comprising an unfiltered full-wave bridge rectifier having inputs connected across the main a.c. power source and having output terminals, a quasi-complementary emitter-follower amplifier having emitterfollower power inputs connected to said bridge rectifier output terminals, a drive control transformer having a primary and a secondary with said primary connected for energization by said operational amplifier active filter output whereby said secondary provides a drive control voltage programmed by said drive signal producing means, and said emitter follower amplifier having a amplifier drive input connected to said drive control transformer secondary and having a power output for connection to a load whereby said power output voltage has an a.c. voltage wave form corresponding substantially to the programmed drive control voltage from said control transformer secondary.